The present invention relates to filamentary reinforced composites, used in applications requiring high strength and/or high modulus of elasticity materials, particularly for high temperature service, and more particularly to boron reinforced composites.
For some 20 years, there has been intensive development of composites with reinforcements utilizing the high strength and high modulus of elemental boron and to a lesser extent the compound system boron carbide, in the form of filaments made by chemical vapor deposition of the reinforcing material on a substrate. The substrate has been primarily selected from refractory metals, and more particularly tungsten. However, cost and weight penalties of tungsten have compelled considerable effort towards provision of a feasible substitute of lesser density and cost, consistent with the necessary conductivity and strength properties. Carbon monofilaments have been found particularly suitable for this purpose but have not afforded sufficient reliability in production to displace tungsten yet.
One approach is substantially given in U.S. Pat. No. 3,679,475 and references therein cited and in my above cited co-pending application and references therein cited.
It is an important object of the invention to provide filamentary reinforcements comprising boron or boron carbide coating on the carbon substrate which is reliably produceable in long lengths.
It is a further object of the invention to enable coating of such carbon substrates without breakage, particularly with boron layers of at least one mil thick and preferably thicker.